The present invention relates generally to the structure of a substrate transport pod suitable for storing or transporting objects such as semiconductor wafers semiconductor wafer manufacturing environment.
In semiconductor wafer manufacturing environment, in order to protect the wafers from particulate contaminants from the ambient sources, the wafers are transported and temporarily stored in hermetically-sealed containers. The hermetically-sealed container for wafers is referred to as a front-opening unified pod (FOUP) and its specifications are standardized internationally.
Conventionally, air-purifying devices remove the moisture and chemical gases from the air inside the FOUP to further protect the wafers from unwanted particulate and chemical contaminants that may enter the FOUP. However, the sealing performance of the FOUP, which is standardized internationally, is insufficient for moisture and chemical gases. When the FOUP is left in a conventional clean room for an extended period of time, some of the moisture and chemical gases in the clean room enter through the ventilation holes furnished in the lower plate of the FOUP and may adhere to the surface of the wafers inside the FOUP. This can result in defective wafers and reduce the production yield.
In some cases, during certain stages of wafer processing, chemicals outgas from the film of organic materials on the wafers being transported in the FOUP and some components of the chemical gases adhere to the interior surfaces of the FOUP. Subsequently, these chemical contaminants may transfer back to the surface of the wafers in the subsequent process steps as the wafers are removed and returned to the FOUP. Such cross-contamination can result in further loss of the wafers due to defects during the manufacturing process. To minimize such cross-contamination concerns, the FOUPs interior can be purged with nitrogen and/or replace the FOUPs with new clean FOUPs during wafer processing. However, such measures are costly.